ARM: omap1: add back omap_set_dma_priority() stub

One of my multiplatform patches went a little too far and removed
a declaration that is needed for compile-testing the omapfb
driver on non-OMAP1 platforms:

arm-linux-gnueabi-ld: drivers/video/fbdev/omap/omapfb_main.o: in function `omapfb_do_probe':
omapfb_main.c:(.text+0x41ec): undefined reference to `omap_set_dma_priority'

Add back the inline stub, and in turn hide the definition when
omapfb is disabled, like we do for the usb specific bits.

Reported-by: kernel test robot <[e-mail]>
Reviewed-by: Tony Lindgren <[e-mail]>
Fixes: 52ef8efcb75e ("dma: omap: hide legacy interface")
Signed-off-by: Arnd Bergmann <[e-mail]>

arch/arm/mach-omap1/omap-dma.c

···
 	omap_writel(l, reg);
 }
 
-#ifdef CONFIG_ARCH_OMAP1
+#if IS_ENABLED(CONFIG_FB_OMAP)
 void omap_set_dma_priority(int lch, int dst_port, int priority)
 {
 	unsigned long reg;
···
 		omap_writel(l, reg);
 	}
 }
-#endif
-
-#ifdef CONFIG_ARCH_OMAP2PLUS
-void omap_set_dma_priority(int lch, int dst_port, int priority)
-{
-	u32 ccr;
-
-	ccr = p->dma_read(CCR, lch);
-	if (priority)
-		ccr |= (1 << 6);
-	else
-		ccr &= ~(1 << 6);
-	p->dma_write(ccr, CCR, lch);
-}
-#endif
 EXPORT_SYMBOL(omap_set_dma_priority);
+#endif
 
 #if IS_ENABLED(CONFIG_USB_OMAP)
 #ifdef CONFIG_ARCH_OMAP15XX

include/linux/omap-dma.h

···
 
 extern struct omap_system_dma_plat_info *omap_get_plat_info(void);
 
+#if defined(CONFIG_ARCH_OMAP1)
 extern void omap_set_dma_priority(int lch, int dst_port, int priority);
+#else
+static inline void omap_set_dma_priority(int lch, int dst_port, int priority)
+{
+}
+#endif
+
 extern int omap_request_dma(int dev_id, const char *dev_name,
 			void (*callback)(int lch, u16 ch_status, void *data),
 			void *data, int *dma_ch);